“This notion of language as a cultural virus is interesting and provocative. And quite possibly true. Certainly, in the vicinity of a modern human mind, language has this character. Language doesn’t emerge spontaneously, like arms or breasts or hair. Those whose access to language is blocked—for example, deaf children who are surrounded by people who speak but don’t sign—usually grow up with little or no language. But when these same children spend their days with others like themselves, the smallest spark of signed language flares and catches through the group as if through dry grassland. Or, if you will, like the measles.”